The Odenwald, along with other parts of the Central German Uplands, belongs to the Variscan orogeny. This mountain ridge across Europe existed more than 300 million years ago during the Carboniferous period. It was eroded and the remains are hilly highlands made of crystalline rocks. But the southern part was downlifted forming the Germanic Basin where massive layers of sedimentary rocks were deposited. The lowest layer is the Early Triassic or Lower Triassic, which consists of reddish sandstones. During the formation of the South German Scarplands the rocks were again eroded, and in the Odenwald area only the lowest level remains and forms the typical landscape of the area. In the northwestern part even the sandstones are eroded and the basement and some granite intrusions can be found on the surface.
Sandstone is not soluble, so there are no karst caves. But the Rhine graben or Upper Rhine Rift is nearby, the downlift created a fracture zone with massive faults. They were filled by groundwater and the precipitation of minerals. And they were the reason for magma intrusions which formed huge granite massives and even volcanism. The heat created convection in the groundwater and the formation of hydrothermal polymetallic ores. The underground sites of this region are mines for those gangue deposits.